Steering apparatus and systems are used for a wide variety of applications from the simplest, that of a bicycle or tricycle, to complex systems used to steer large aircraft and seagoing vessels. As the "human input device," such systems may use simple handlebars, a lever-like tiller with freedom of movement in one or two axes, or a steering wheel or steering segment, i.e., a portion of a wheel, the latter as often used on aircraft. A steering segment or wheel is popular since its motion and the result of such motion, vehicle steering left or right, is very familiar to drivers of motor vehicles.
A reason for such popularity is that use of a steering wheel is almost intuitive. One is far less likely to make a steering error when using a steering wheel than, for example, when using a push-pull rod. Recalling whether "in" or "out" movement of such rod provides left or right direction steering can be problematic, especially in an emergency steering situation.
Notwithstanding the popularity and obvious utility of the wheel as a steering device, the "end function" component, e.g., a steerable boat jet or rudder, often requires application of linear force and resulting linear movement to effect steering. This fact is recognized by certain prior art steering apparatus such as depicted in U.S. Pat. Nos. 5,018,469 (Carlson) and 4,501,218 (Teraura et al.). The Carlson and Teraura et al. patents both show rack-and-pinion drives for converting rotary motion into linear motion.
A pinion-drive steering apparatus is depicted in a document titled "New Jet Boat Steerer" by Morse Controls Div. IMO Industries. Such apparatus provides diminishing steering forces and reduced steering rate as the steering wheel is turned farther from its center position.
While these earlier steering apparatus have been generally suitable for their intended purpose, they have certain disadvantages. One such disadvantage is that they are relatively expensive to manufacture. Of course, higher manufacturing costs translate into higher selling prices, a fact which users of such apparatus prefer to avoid. As examples, worm gear drives and rack-and-pinion drives require several carefully machined, "close tolerance" parts. And equipment for cutting gear teeth is relatively expensive.
Yet another disadvantage relates to "design flexibility." The purchaser of the apparatus, e.g., an original equipment manufacturer (OEM) of boats, is likely to have varying requirements relating to steering torque, magnitude of output force, stroke length, direction of output stroke for a given direction of steering wheel rotation, and so forth, depending upon the size and type of boat and the configuration of its drive components. When the steering apparatus uses gear-like parts, it is difficult to configure the apparatus to meet a broad range of requirements of the type noted above.
Still another disadvantage arises from certain specific types of geared steering apparatus. Here are some examples. A rack-and-pinion steering apparatus (of the type depicted in the above-noted Carlson patent) or a cable-and-pulley apparatus as shown in U.S. Pat. No. 5,136,894 (Carter et al.) provides output force and motion along an axis which is 90.degree. to the long axis of the steering column shaft. Many applications are better suited for an arrangement in which the output force is available along an axis parallel to the steering column shaft.
Other disadvantages relate to aspects of "steering rate," i.e., the length of linear movement of the output device for a given number of degrees of rotation of the input device, e.g., the steering wheel. Steering apparatus of the worm drive type seemingly require several revolutions of the steering wheel to produce a relatively short output movement. The diminished steering rate characteristic of the apparatus depicted in the Morse Controls document may be unsuited for certain jet boat applications which need increased steering rate with greater excursions of the steering wheel from center. And in any event, the known prior art does not offer "variable rate" steering, i.e., a steering rate which changes depending upon how far the steering wheel is rotated from a "straight ahead" or center position.
Yet another disadvantage to certain of the prior art steering apparatus relates to size and weight. They are simply too heavy, cumbersome and bulky to be of much value in, say, small water craft and ultralight aircraft. And weight and bulk often imply difficulty in repair.
An improved steering apparatus which addresses the aforementioned disadvantages would be an important advance in the art.